Low friction snap-acting thermostat



Dec. 28, 1965 c, s. MERTLER 3,226,511

LOW FRICTION SNAP-ACTING THERMOSTAT Filed Dec. 31, 1962 2 Sheets-Sheet 1 INVENTOR. CHARLES S. MERTLEI'? Wm y Dec. 28, 1965 c s. MERTLER 3,226,511

LOW FRICTION SNAP-ACTING THERMOSTAT Filed D80. 51, 1962 2 Sheets-Sheet 2 INVENTOR. CHARLES S. MERTLER BY Wan 7, W

M M W.

United States Patent Ofitice 3,226,511 LOW FRICTION SN AFP-ACTIN G THERMOSTAT Charles S. Mertler, Mansfield, Ohio, assignor to Stevens Manufacturing Company, Inc, a corporation of Ohio Filed Dec. 31, 1962, Ser. No. 248,639 8 Claims. (Cl. filo-138) The invention relates in general to snap-acting thermostats and more particularly to one having low friction between relatively movable parts to achieve superior operating characteristics.

The invention may be incorporated in a snap-acting thermostat having a snap-acting over-center contact blade carried on a base with a first contact on this blade. A second contact is carried on the base for cooperation with the first contact. A thermally actuated blade is mounted to have an outboard end which is connected to the outboard end of the contact blade by link means to relatively move the contacts upon temperature changes.

The prior art snap-acting thermostats typically had a much wider temperature differential between off and on conditions of the contacts than did creep action thermostats. Snap-action thermostats were used in those applications wherein the wider temperature differential could be tolerated and wherein the snap-action of the contacts was preferred over the creep action movement, for example, in high current or inductive current applications where the snap-acting movement helped to extinguish any are.

Also, the prior art snap-acting devices in many cases had only a minimum contact separation after snapping over to the off condition in order to minimize this temperature differential and this minimum contact separation limited the voltage and inductive current rating of the thermostat.

A typical prior art snap-acting thermostat was as shown in the Edward Bletz Patent 2,692,317 issued October 19, 1954, to the same assignee as the instant application. This snap-acting thermostat had an insulating button made of ceramic, for example, and carried by the outboard end of the bimetal blade to act on the rear of a contact-carrying blade. As the bimetal blade warped during temperature changes, the insulator button had to scrape longitudinally along the rear face of this contact blade in order to bend same and this was a major source of friction within the thermostat before the contacts would snap over center to the opposite condition. Thus, the bimetal blade not only had to do work to overcome the spring stress within the contact blade but also had to do work overcoming this friction. Other types of prior art snap-acting devices had a snap-acting member which was separate from the Contact carrying member and these two parts had longitudinal friction therebetween as they moved to obtain the over center snap-action. Again, this was a major portion of the friction in the thermostat which had to be overcome by the force of the warping bimetal and thus contributed greatly to the large temperature differential.

An object of the present invention is to obviate the above-mentioned deficiencies and to produce a snap-acting thermostat of superior characteristics.

Another object of the invention is to provide a snapacting thermostat of very low internal friction to achieve a low temperature differential.

Another object of the invention is to provide a snapacting thermostat which has a low mass of moving parts to minimize temperature differential.

Another object of the invention is to provide a snapacting thermostat wherein a thermally responsive member is mounted on one end of the thermostat near the mount ing surface for mounting to a support and an adjustment 3,226,511 Patented Dec. 28, 1965 screw is mounted on the other end of the thermostat and with the adjustment screw passing through apertures in the thermally responsive member and through contact blades controlled by said thermally responsive member.

Another object of the invention is to provide a snapacting thermostat with movable parts having a line contact to minimize friction during changes of attitude between the moving parts.

Another object of the invention is to provide a snapacting thermostat which has a large contact separation for higher voltage and higher inductive current applications yet retaining a low temperature differential between off and on conditions.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a the invention;

FIGURE 2 is a side elevational view partially in section of the thermostat of FIGURE 1;

FIGURE 3 is a bottom view of the thermostat;

FIGURE 4 is an end view of the insulating push link with contact blade 15 omitted;

I FIGURE 5 is an enlarged partial side view partially in section, with contact blade 15 omitted;

FIGURE 6 is a plan view of the snap-acting blade removed from the thermostat;

FIGURE 7 is a side elevational View of a modified form of thermostat; and,

FIGURE 8 is a plan view of the modified form of snap link in FIGURE 7 but removed from the thermostat.

The figures of the drawing show a thermostat 11 in which the invention may be incorporated with this drawing for purposes of illustration and not limitation. The thermostat 11 includes generally a base 12 on which is carried a stack 13. The stack includes first and second contact blades 14 and 15 and a mounting blade 16. The first and second contact blades 14 and 15 carry first and second contacts 17 and '18, respectively, mounted for mutual cooperation on the outboard ends of these blades. The various blades are mounted in the stack 13 and the contact blades 14 and 15 are mutually insulated and insulated from the stack by use of insulating washers 19. Terminals 20 and 21 are provided in the stack 13 for external connection to the first and second contact blades 14 and 15. The stack 13 is held together with a rivet 22 having a head 23 and a formed head 24 at the base 12. The rivet 22 may be hollow to receive a mounting screw, not shown, to mount the thermostat 11 in a conventional manner with the head 23 against a support. The rivet 22 has an axis 25. The first contact blade 14 is shown removed from the thermostat in FIGURE 6, and is a snap-acting over-center blade. It is normally biased downwardly with contact 17 engaging contact 18, as caused by an upwardly dished portion 60 formed in the mid-portion of the blade 14.

A bimetal blade 29 is fixed to the mounting blade 16 by a rivet 28 which has a socket 39. This socket receives an insulator tip 31 of an adjusting screw 32 threaded in a nut 33 fixed on the base 12. The screw 32 on the tip 31 passes through apertures in the blades 14, 15 and 16. An extending tongue 34 protrudes from an enlarged tongue 35 on the bimetal blade 29. An extending tongue 36 protrudes from an enlarged tongue 37 on the contact blade 14. An insulating push link or operating link 38, for example of porcelain material, has apertures 39 and 40 to receive these enlarged tongues 35 and 37, respectively. The extending tongues 34 and 36 are bent to retain the push link 33 on the ends of the blades 14 and 29.

plan view of a thermostat embodying The length of the enlarged tongue 35 is approximately the same as the thickness of the link 38 and this link is closely restricted longitudinally by the turned down tongue 34. The enlarged tongue 35 restricts sideways movement of the insulating push link 38. The end of the first contact blade 14 has a similar construction and this permits the insulating link 38 to be loosely yet closely and positively connected to both the contact blade 14 and bimetal 7 blade 29.

The thermostat 11 may be either single pole, single throw or single pole, double throw, as shown. For this double throw feature, an extra contact blade 41 is mounted in the stack 13 and carries a third contact 42 to cooperate with a fourth contact 43 on contact blade 14 on the side opposite the first contact 17. The base is threaded to receive an abutment screw 44 having an insulator tip 45 to abut the rear of the third contact blade 41. The third contact blade 41 is resiliently biased by its mounting in the stack 13 to be urged toward the abutment screw 44. Thus, adjustment of this screw 44 provides an adjustable abutment limit for this third contact 42.

The bimetal blade 29 deflects upwardly on temperature change and this may be an increase in temperature, for example. The thermostat 11 is shown in its normal position with the contacts 17 and 18 in engagement. Upon temperature change, the bimetal blade 29 warps upwardly and pushes through the push link 38 to urge the snap-acting blade 14 upwardly. At some point it will overcome the downward urging of blade 14 and this blade 14 will snap over to open the contacts 17 and 18 and close the contacts 42 and 43. Thus, the position of the abutment screw 44 provides an adjustable abutment limit for the alternate over-center position of the over-center contact blade 14. The second contact blade 15 is relatively rigid to provide a limit for the first over-center position of the snap-acting contact blade 14. When the birnetal blade 29 cools and the upward urging force is reduced, the snap-acting blade 14 will again snap to its lower position engaging contacts 17 and 18.

The base 12 also includes another adjustment screw 48 acting on a deflecting blade 49 having a forked end on the upwardly curved mid-portion 26 of the snap-acting contact blade 14. Adjustment of this screw 48 adjusts the snapping pressure of the contact blade. 14 by adjusting the point at which this snap-acting blade will snap over center. The abutment screw 44 adjusts the contact gap and also adjusts the operating temperature differential between open and closed conditions of the contacts.

FIGURE 6 shows the snap-acting over-center contact blade 14 as removed from the thermostat. This snapacting blade 14 has an upwardly convex dished portion 60 formed therein which establishes the outboard end of this contact blade curved slightly downwardly. The contact blade 14 then may be normalized or stress relieved to establish that the blade 14 inherently tries to return to this downwardly curved position, see FIGURE 2, even after the outer end of the blade 14 has been snapped upwardly through a snap-plane to a second position. The first position is as shown in FIGURE 2 with the outer end of the blade 14 curved downwardly. The contact blade 14, during manufacture, may next be given another additional upward convex bumping force at the dished portion 60 to make this blade 14 act as a snap-acting over-center blade. This establishes that the blade 14 not only will snap over center but always tries to return to the first or downwardly curved position.

If the snap acting blade 14 is removed from the thermostat, as shown in FIGURE 6, then the blade may have a certainand definite requirement of upward force on the outboard end to make it snap over center. For example, this might be fifteen ounces of force and after it has been snapped over center there is another return force inherent in the blade 14 because of the dished portion 60 and this return force may be, for example, three ounces. When the contact blade 14 is assembled in the thermostat, these forces change to six ounces and two and one-half ounces, for example, because of the relatively rigid second contact blade 15 which deflects upwardly the outboard end of the snap acting blade 14, and the deflecting blade 49 acting downwardly on the convex dished portion 60. Accordingly, the upward force required for snap-over on the outboard end of the contact blade 14 is reduced to about six ounces for example. When the bimetal blade 29 undergoes temperature change to cause it to try to deflect upwardly, energy is stored in this bimetal blade until it exerts a force just equal to the aforementioned downward force or initial bias in the snap acting blade 14. When the upward force from the stored energy in the bimetal blade 29 just exceeds the downward force inherent in the contact blade 14, then this contact blade 14 snaps over center. Because of the snap movement, the force built up in the bimetal blade is reduced, for example to four ounces.

Because of the assembly of the blade 14 into the thermostat and the forces exerted by the deflecting blade 49 and the contact blade 15, the downward return force inherent within the contact blade 14 is reduced from its former amount, for example three ounces, to a lower value, for example two and one-half ounces. Now, when the temperature changes in the opposite direction, the bimetal blade 29 cools and the upward force then reduces from its former amount of four ounces to just below two and one-half ounces, at which time the contact blade downward force overcomes the upward force of the bimetal blade 29 to cause it to snap downwardly to the first position. Accordingly, it will be seen that only a very small differential force need be built up in the bimetal blade 29 to cause actuation of the thermostat 11.

FIGURE 5 best shows the fact that the insulating push link 38 has generally a line contact 52 with the bimetal blade 29 and a line contact 53 with the first contact blade 14. This line contact at each end of the insulating link 38 minimizes the friction during movement of all parts of the thermostat 11. As the bimetal blade 29 warps upwardly during temperature change, it pushes on the push link 38 and upon overcoming the downward resilient force in the contact blade 14, it causes the contact blade 14 to snap over center. During this snap-acting movement, the insulating link 38 travels generally longitudinally of its length which is substantially parallel to the axis 25. Because the movement is generally along the length of the push link 38, there is a minimum of change of attitude between the push link 38 and the blades 29 and 14 and also these line contacts 52 and 53 have a minimum rocking action thereat. This establishes the minimum friction so that the thermostat 11 has a very small temperature differential between open and closed switch conditions.

The FIGURE 4 shows that the push link 38 actually holds apart the contact blade 14 and bimetal blade 29. This is because the bimetal blade 29 is mounted to have an upward bias or urging force, and in the normal position, the contact blade 14 has a downward bias. The snap-acting contact blade 14 when completely removed from the thermostat 11 will have considerably more curvature than shown in FIGURE 2. In one embodiment in accordance with the invention this contact blade 14 required about ll ounces of force to snap it over center when this contact blade 14 was in a free condition as removed from the thermostat. However, as restrained in the thermostat 11, the deflecting blade 49 pushes downwardly on the center .and the relatively rigid second contact blade 15 pushes upwardly at the outer end. Thus the contact blade 14 is close to the position and condition of snapping over center. Accordingly, only about two ounces of differential force may be required from the bimetal blade 29 to cause the contact blade 14 to snap over center. The minimum friction achieved by the construction of the thermostat is primarily responsible for this low opera-ting force, and in turn provides the very small temperature differential.

The insulating link 38 is shown as a push link to hold apart the contact blade 14 and bimetal blade 29. If the contact blade 14 were turned upside down in the thermostat 11 so that its initial bias caused it to engage contact 42, then the bimetal blade 29 could pull downwardly to cause snap action in the downward movement and, accordingly, the insulating link 38 would be .a pull link rather than a push link.

The U-shape of the bimetal blade 29 permits a considerably longer length of bimetal and, accordingly, a heavier thickness of bimetal for more operating force, yet within a small, compact thermostat. Accordingly, the thermostat may readily be used on heavier power applications, for example, 240 volts and 25 ampere service. This longer length bimetal is provided in a thermostat 11 of quite compact dimensions without any overhang of the mounting of the bimetal and yet this permits mounting 'of the bimetal blade 29 on the resilient mounting blade 16. This resilient mounting blade 16 permits change in mounting attitude of the bimetal blade 29 by the adjustment screw 32 for adjustments of temperature. Accordingly, it will be noticed that the snap plane of the snap acting contact blade 14 is not changed as the thermostat 11 is changed in adjustment of the operating temperature. This again permits superior operating characteristics compared to the prior art patents such as Patent 2,692,317.

This construction of the thermostat 11 permits a compact thermostat of high current and voltage rating. The base 12 carries the stack 13 and the bimetal blade 29 is mounted adjacent the rivet head 23 which is the mounting surface of the thermostat 11 to a support. This may be by a bolt or screw passing through tthe hollow rivet 22 to secure the thermostat 11 to such support. Such support is usually metallic subject to heat from a heater as controlled by the thermostat 11 by means of opening and closing the contacts. The adjusting nut 33 is mounted on the base 12 on the side opposite the mounting surface 23. The adjusting screw 32, or as shown the insulating tip 31 thereof, passes through apertures in each of the contact blades 14, and 41 .and through an aperture in the bimetal blade 29. This construction permits the adjusting screw to be on the opposite end of the thermostat from the mounting surface 23 yet to control the adjusted position of the bimetal blade 29 with this bimetal blade 29 being adjacent the support to which the thermostat 11 is fastened. This permits good heat transfer to the bimetal blade and ready access to the adjusting screw 32. This desirable result is obtained without changing the snap plane of the snap acting contact blade 14 during adjustment.

It will be noted that the temperature changes tend to warp the creep action bimetal blade 29 until enough energy is stored in the bimetal blade 29 to cause snap-over movement of the contact blade 14. Accordingly, the adjustment screw 32 is in series with the thermally responsive member 29 and which also includes an energy storage means, and this series combination is connected between the base 12 and the snap acting contact blade 14.

The prior art patents, such as Patent 2,692,317, typically had an insulating button rigidly secured to the bimetal blade and merely abutting a contact blade. Thus, as the bimetal blade warped under temperature change, the insulating button was frictionally dragged along the surface of the contact blade, generally in a longitudinal direction, in order to cause this contact blade to snap over. This sliding friction was a large factor in the amount of work required to be done by the bimetal blade, and contributed in large measure to the large temperature differential of the prior art thermostats. Another form of prior art snap-acting thermostat was wherein the contact blade, such as contact blade 14, was not snap-acting, instead it was a creep action cantilever blade. A separate snapacting member was adjacent thereto to provide the snapaction but there was the inherent sliding friction between such contact blade and the snap-acting member. Accordingly, in this design as well, there was a large sliding friction to be overcome by work expended by the bimetal blade, This type of prior art thermostat also had a large temperature differential contributed in large measure by the sliding friction.

The thermostat of the present invention minimizes the friction and also minimizes the mass to be moved by the bimetal blade 29, and accordingly a small temperature differential is achieved. Applicant has constructed a thermostat in accordance with the present invention generally as shown in the drawing, which has a .010 inch contact separation and with only a two to three degree temperature differential on the bimetal blade 29. This contrasts with typical prior art constructions which had a ten to fifteen degree bimetal differential and this with only a .002 inch or .003 inch contact separation. If the limit, such as abutment screw 44, were adjusted in the prior art devices to achieve a .010 inch contact separation, the bimetal differential would be even higher than ten to fifteen degrees. The large contact separation of .010 inch in the present device permits operation at higher voltages and higher current carrying capacities and permits operation at 240 volts and 25 amperes.

The practically complete elimination of friction in operation of the thermostat 11 has another desirable feature, namely, the improvement in repeatability. As the temperature cycles from on to off and back to on again, in response to temperature of the appliance with which it is used, the temperature of all the on points is much more uniform than formerly. This is also true of the temperature of all the off points as well. In other words, the cycling of the thermostat is much more uniform since the friction has been made very much lower than formerly and this was the big variable as far as establishing the point at which the contact blade snapped over center. Since this large variable has been removed or greatly minimized, the repeatability of the cycling temperature is vastly improved.

FIGURES 7 and 8 show another modification of the invention as embodied in a thermostat 11A. This thermostat 11A is similar to the thermostat 11 except that it embodies a snap-acting contact blade 64 instead of the contact blade 14. This contact blade 64 is better shown in FIGURE 8. The outboard end of the contact blade 64 carries the first contact 17. The contact blade 64 is a three-legged blade having first, second and third legs 65, 66 and 67. A flanged hole 68 is provided in the middle leg 66 for passage of the insulator end 31. A deflecting blade 69 is carried in the stack 13 and may be fixed to the middle leg 66 as by the rivet 70. The adjusting screw 48 bears against this deflecting blade 69. V-crimps 71 are provided in the outer legs 65 and 67 to shorten these legs and thus make the contact blade 64 a snap acting over-center blade. During manufacture, the snap-acting contact blade 64 may be bent to have a downward curva ture at the outer end carrying the contact 17. This blade may then be normalized to relieve stresses and so that it will tend to return to this initial downward bias. Next, the V-crimps 71 may be put in the outer legs 65 and 67 to make this a snap-acting blade but one which tends to return to the first or downward position upon being snapped upwardly through a snap plane to a section position. This thermostat 11A with the contact blade 64 will operate in essentially the same manner as thermostat 11 of FIGURES 1-6.

Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinatfer claimed.

What is claimed is:

1. A friction-free snap-acting thermostat comprising, in

combination, a base,

a snap-acting over-center contact blade having a mounting portion carried on said base,

a first contact carried on said contact blade,

a second contact,

a second contact blade mounting said second contact on said base for cooperation with said snap acting first contact,

means including said second contact blade to substantially rigidly position said second contact,

means to bias said contact blade to an over-center position urging said contacts together,

a bimetal blade having a mounting portion and an outboard end,

a resilient arm carrying said bimetal blade mounting portion and having a portion fixed on said base,

a socket at the outboard end of said resilient arm,

said bimetal blade being doubled into a U-shape and the outboard end thereof extending outwardly beyond the outer end of said second contact blade,

adjustment means extending through apertures in said contact and bimetal blades and adjustable relative to said base to engage said socket in said resilient arm to adjust the position of said bimetal blade,

and an insulating link loosely and positively connected at the two ends thereof to the outboard ends of said snap-acting contact blade and said bimetal blade to move said contact blade in accordance with movement of said bimetal blade.

2. A friction-free snap-acting thermostat comprising,

in combination, a base,

a snap-acting over-center contact blade and a bimetal blade each having a mounting portion carried on said base,

a first contact carried on said contact blade,

a second contact,

means to mount said second contact on said base for cooperation with said first contact,

said contact blade having an initial bias urging same to a first position on one side of a snap-plane and establishing a return force to said first position upon being snapped over-center to a second position on the other side of said snap plane,

a socket on said bimetal blade,

adjustment means adjustable relative to said base to engage said socket to adjust the position of said bimetal blade,

an insulating link loosely and positively connected at the two ends thereof to the outboard ends of said contact blade and said bimetal blade,

an adjustment abutment carried relative to said base to limit over-center movement of said contact blade, and temperature changes of said bimetal blade tending to move same in a creep action and storing energy therein against said initial bias of said over-center contact blade until the stored energy force exceeds said initial bias to cause snap acting movement of said contact blade to said second position.

3. A friction-free snap-acting thermostat comprising, in

combination, a base,

a snapacting over-center contact blade and a bimetal blade each having a mounting portion carried on said base,

a first contact carried on said contact blade,

a second contact,

means to mount said second contact on said base for cooperation with said first contact,

a resilient arm carrying said bimetal blade and having a portion fixed on said base,

a socket at the outboard end of said resilient arm,

adjustment means adjustable relative to said base to engage said socket in said resilient arm to adjust the position of said bimetal blade,

said bimetal blade beingdo'ubled into a U-shape and the outboard end thereof extending outwardly beyond said second contact,

and an insulating link loosely and positively connected at the two ends thereof to the outboard ends of said contact blade and said bimetal blade.

4. A friction-free snap-acting thermostat comprising, in

combination, a base,

first and second contact blades and a bimetal blade disposed in that order and each having a mounting portion carried on said base,

said first contact blade being a snap-acting over-center blade,

said second contact blade being relatively rigid,

said first and second contact blades carrying first and second contacts, respectively, for mutual cooperation,

means to bias said first con-tact blade to an over-center position urging said contacts together,

a resilient arm carrying said bimetal blade and having a portion fixed on said base,

a socket at the outboard end of said resilient arm,

said bimetal blade being doubled into a U-shape and the outboard end thereof extending outwardly beyond the outer end of said second contact blade,

an insulating link interconnecting the outboard ends of said first contact blade and said bimetal blade,

a nut fixed on said base,

a screw threaded in said nutand extending through apertures in said contact blades and said bimetal blade to engage said socket on said resilient arm,

and an adjustable abutment carried relative to said base to act as a limit for movement of said first contact blade upon snapping over center whereby heating of said bimetal blade moves same toward first contact blade and said insulating link causes concurrent movement of said snap-acting first contact blade to snap same over center to the open condition of said contacts.

5. A snap-acting thermostat comprising, a combination,

a base,

a snap-acting over-center contact blade and a creep action bimetal blade each having a mounting portion carried on said base,

a first contact carried on said contact blade,

a second contact,

means to mount said second contact on said base for cooperation with said first contact,

said contact blade having an initial bias urging same to a first position on one side of a snap-plane and establishing a return force to said first position upon being snapped over-center to a second position on the other side of said snap plane,

said bimetal blade being doubled into a U-shape and the outboard end thereof extending outwardly beyond said second contact,

means interconnecting the outboard ends of said contact blade and said bimetal blade,

and temperature changes of said bimetal blade tending to move same in a creep action and storing energy therein against said initial bias of said over-center contact blade until the stored energy force exceeds said initial bias to cause snap acting movement of said contact blade to said second position.

6. A snap-acting thermostat comprising, in combination, a base,

a stack fixed on said base, I

a snap-acting over-center contact blade and a second contact blade each having a mounting portion carried in said stack,

a first contact carried on said snap-acting blade,

a second contact carried on said second contact blade for cooperation with said first contact,

means including said second contact blade to substantially rigidly position said second contact,

a resilient arm carrying a bimetal blade and having a portion fixed in said stack,

said stack having a mounting surface opposite said base,

means to mount said stack mounting surface to a support with said bimetal blade adjacent said support,

a socket at the outboard end of said resilient arm,

adjustment means carried on said base and extending through apertures in said blades to engage said socket in said resilient arm to adjust the position of said bimetal blade,

and means to move said snap-acting contact blade in accordance with movement of said bimetal blade.

7. A friction-free snap-acting thermostat comprising,

in combination, a base,

a snap-acting over-center contact blade having an outboard end and having a mounting portion carried on said base,

first, second, third and fourth contacts,

means to mount said first and fourth contacts on said contact blade,

means to mount said second and third contacts on said base for cooperation with said first and fourth contacts, respectively,

said contact blade having an initial bias urging same to a first position on one side of a snap-plane and establishing a return force to said first position upon being snapped lover-center to a second position on the other side of said snap plane,

a bimetal blade having a mounting portion and an outboard end,

a resilient arm carrying said mounting portion of said bimetal blade and fixed on said base,

means interconnecting the outboard ends of said contact blade and said bimetal blade,

and adjustable abutment means including said third contact to limit over-center movement of said contact blade whereby temperature change of said bimetal blade tends to move same and stores energy therein against said initial bias of said snap-acting contact blade until the stored energy force exceeds said initial bias to cause snap acting movement of said contact blade to a position closing said third and fourth contacts.

8. A friction-free snap-acting thermostat comprising, in

combination, a base,

a stack fixed on said base,

first and second contact blades and a bimetal blade disposed in that order relative to said base and each having a mounting portion,

means fastening the mounting portions of said contact blades in said stack,

said first contact blade being a snap-acting over-center blade,

said second contact blade being relatively rigid,

said first and second contact blades carrying first and second contacts, respectively, for mutual cooperation,

means to bias said first contact blade to an over-center position urging said contacts together,

a resilient arm carrying the mounting portion of said bimetal blade and having a position fixed in said stack,

a socket at the outboard end of said resilient arm,

said bimetal blade being doubled into a U-shape and the outboard end thereof extending outwardly beyond the outer end of said second contact blade,

an insulating push link loosely but closely and posi tively interconnecting the outboard ends of said first contact blade and said bimetal blade,

a nut fixed on said base,

a screw threaded in said nut and extending through apertures in said contact blades and said bimetal blade to engage said socket in said resilient arm,

and an adjustable abutment carried in said base and acting on the outboard end of said first contact blade on the side opposite said first contact whereby heat ing of said bimetal blade moves same toward said base and said insulating link causes concurrent movement of said snap-acting first contact blade to snap same over center to the open condition of said contacts.

References Eited by the Examiner OTHER REFERENCES Widmaier German application, 1,077,333, March 10,

BERNARD A. GILHEANY, Primary Examiner. 

1. A FRICTION-FREE SNAP-ACTING THERMOSTAT COMPRISINT, IN COMBINATION, A BASE, A SNAP-ACTING OVER-CENTER CONTACT BLADE HAVING A MOUNTING PORTION CARRIED ON SAID BASE, A FIRST CONTACT CARRIED ON SAID CONTACT BLADE, A SECOND CONTACT, A SECOND CONTACT BLADE MOUNTING SAID SECOND CONTACT ON SAID BASE FOR COOPERATION WITH SAID SNAP ACTING FIRST CONTACT. MEANS INCLUDING SAID SECOND CONTACT BLADE TO SUBSTANTIALLY RIGIDLY POSITION SAID SECOND CONTACT, MEANS TO BIAS SAID CONTACT BLADE TO AN OVER-CENTER POSITION URGING SAID CONTACTS TOGETHER, A BIMETAL BLADE HAVING A MOUNTING PORTION AND AN OUTBOARD END, A RESILIENT ARM CARRYING SAID BIMETAL BLADE MOUNTING PORTION AND HAVING A PORTION FIXED ON SAID BASE, A SOCKET AT THE OUTBOARD END OF SAID RESILIENT ARM, SAID BIMETAL BLADE BEING DOUBLED INTO A U-SHAPE AND THE OUTBOARD END THEREOF EXTENDING OUTWARDLY BEYOND THE OUTER END OF SAID SECOND CONTACT BLADE, ADJUSTMENT MEANS EXTENDING THROUGH APERTURES IN SAID CONTACT AND BIMETAL BLADES AND ADJUSTABLE RELATIVE TO SAID BASE TO ENGGE SAID SOCKET IN SAID RESILIENT ARM TO ADJUST THE POSITION OF SID BIMETAL BLADE, AND AN INSULATING LINK LOOSELY AND POSITIVELY CONNECTED AT THE TWO ENDS THEREOF TO THE OUTBOARD ENDS OF SAID SNAP-ACTING CONTACT BLADE AND SAID BIMETAL BLADE TO MOVE SAID CONTACT BLADE IN ACCORDANCE WITH MOVEMENT OF SAID BIMETAL BLADE. 